Suitable methods of supervising a fetus and a mother before and during labor include the monitoring of the fetal heart rate. This monitoring of the fetal heart rate is non-invasive, and enables observation of fetal activity in realtime.
The method of detection of the fetal heart rate employed in the monitoring of a fetus is roughly classified into two types: one, an external measurement and the other, an internal measurement. The outer measurements include (1) fetal phonocardiography, (2) ultrasonic Doppler method, and (3) mother absomen induced fetal electrocardiography. The internal measurements include infant head induced fetal electrocardiography.
Among these methods, it is the ultrasonic Doppler method which ensures the most effective detection of the fetal heart rate during the NST (non stress test). The second best detection method is the fetal phonocardiography, with the mother abdomen induced fetal electrocardiography being the worst. In the infant head induced fetal electrocardiography, which is the internal measurement, spiral shaped electrodes have to be directly attached to the head of the infant. So, this method can be used only after the amniorrhexis or a rupture of membranes: it cannot be used before delivery. Thus, monitoring of the fetal heart rate which employs any of the external measurements is most useful for fetal observation which is conducted during the NST, because it allows fetal activity to be detected non-invasively in realtime.
Generally, the requirements of the fetal monitoring apparatus are as follows:
I: It must be portable. PA0 II: Since both the fetus and the mother have to be observed, it permits an observer to grasp the present conditions at a glance. At the same time, detailed data can be extracted whenever required. PA0 III: It can also be utilized to monitor the twin that occurs occasionally. PA0 IV: An alarm may be issued to draw the observer's attention and thereby help him determine fetal activity when the fetal heart rate exceeds a certain value. It is capable of issuing various types of alarms, depending on the present conditions of the mother and the fetus.
Next, how the conventional fetal monitoring apparatus fulfills the above-described requirements, together with its shortcomings or problems, will be described below.